Air source heat pump (ASHP) water heaters are efficient devices for sanitary hot water heating. The coefficient of performance (COP) of the air to water heat pump (AWHP) is constantly lower than that of the corresponding ASHP unit. The study focused on determining the COP of both the ASHP unit and the AWHP. This was achieved by the implementation of both experimental and simulation methods, with the help of a data acquisition system and the REFPROP software. The system comprised of a 1.2 kW split type ASHP unit and a 150 L high pressure geyser. A power meter, flow meters, temperature sensors, pressure sensors, ambient temperature and relative humidity sensor were installed at precise locations on the split type AWHP. Controlled volumes of 150, 50 and 100 L were drawn off from the AWHP during the morning, afternoon and evening for a year. The average COP for the summer and winter, in terms of the input electrical and output thermal energies of the AWHP were 3.02 and 2.30. The COPs of the ASHP unit, in terms of the change in the enthalpies of the refrigerant at the inlet and the outlet of the condenser and the evaporator, were 3.52 and 2.65 respectively. The study showed that the difference between the COP of the ASHP unit and that of the AWHP could be ascribed to the electrical energy consumed by the fan and the water circulation pump during the vapour compression refrigeration cycles. The work provides an energy optimisation opportunity to the manufacturers of this technology, helping to enhance the efficiency and COP of ASHP water heaters. Highlights The COPt of the ASHP unit was higher than the COPe of the AWHP. The COPe of the AWHP was the ratio of the input electrical energy consumed and the output thermal energy gained by the stored water. The COPt of the ASHP unit was enthalpies-dependent and a function of inlet and outlet enthalpies of the evaporator and condenser. The inlet and outlet refrigerant temperatures profiles of the condenser confirmed thermal energy dissipation.

Biogas is among the sources of renewable energy with a great potential to mitigate global energy challenges by virtue of the ease of implementation of the technology. The study focused on monitoring the total viable bacteria counts with the number of days, daily average ambient temperature and pH from a balloon type biodigester fed with 2500 L of cow manure (500 L of slurry each day for five successive days) with six months retention time using data acquisition system, standard methods and mathematical model. A non-linear response surface model was developed to predict the total viable bacteria counts with the predictors. The predictors were ranked by weights of importance to the desired targets by reliefF test. At the end of the anaerobic digestion cycle the cumulative volume of biogas was 6.75 m³ with 65.8% methane and 31.2% carbon dioxide. The ranking by weights of the predictors revealed that all the input parameters were primary factors and number of days contributed the most. Based on the testing data set, the response surface model was capable of predicting the total viable bacteria counts with high accuracy as the determination coefficient, root mean square error and p-value were 0.959, 0.197 and 0.602.

Purpose: This paper aims to show that by using air source heat pump (ASHP) water heater in the residential sector, the energy consumption from sanitary hot water production can be reduced by more than 50 per cent. Hence, this study quantitatively and qualitatively confirms that domestic ASHP water heater is a renewable and energy efficient device for sanitary hot water production. Design/methodology/approach: Design and building of a data acquisition system comprises a data logger, power meters, flow meters, temperature sensors, ambient and relative humidity sensor and an electronic input pulse adapter to monitor the ASHP water heater performance. All the sensors are accommodated by the U30-NRC data logger. The temperature sensors are installed on the inlet pipe containing a flow meter and the outlet pipe of the ASHP unit, the vicinity of both evaporator and expel cold air. An additional temperature sensor and a flow meter that cater for hot water drawn off measurements are incorporated into the data acquisition system (DAS). Findings: The result from a specific monitoring split type ASHP water heater gives an average daily coefficient of performance (COP) of 2.36 and the total electrical energy of 4.15 kWh, and volume of hot water drawn off was 273 L. These results were influenced by ambient temperature and relative humidity. Research limitations/implications: The cost involved in purchasing the entire sensors and data logger limits the number and categories of ASHP water heaters whose performance were going to be monitored. Pressure sensors were excluded in the data acquisition system. Practical implications: The data acquisition system can easily be designed and the logger can also be easily programed. Hence, no high technical or computer skills are needed to install the DAS and to be able to read out the results. Social implications: Hence, the data acquisition system can be installed on the entire domestic Eskom roll out air source heat pump water heaters to effectively determine the coefficient of performance and demand reductions. Originality/value: This DAS is the first of its kind to be built in South Africa to be used to determine the performance of an ASHP water heater with high accuracy and precision. DAS is also robust.